On 1/12/26 5:01 PM, Eelco Chaudron wrote:
>
>
> On 6 Jan 2026, at 15:31, Dumitru Ceara via dev wrote:
>
>> OVN relies heavily in its OpenFlow rules on the registers that are
>> provided by OVS. With the OVN feature set increasing we are slowly but
>> surely running out of register space.
>>
>> The suggestion to increase the number of OVS registers again (last time
>> this happened was with 847b8b027af4 ("Increase number of registers to
>> 16.")), keeps being brought up on the mailing list, most recently in [0]
>> and [1]. The alternative would be to work around the register space
>> issue in OVN by using approaches like pushing/popping registers to the
>> stack. But that would complicate the OVN pipeline even further.
>>
>> Instead this patch increases the number of general purpose 32-bit
>> registers to 32. That implies that the number of 64-bit registers
>> (xreg) also increases to 16 and the number of 128-bit registers (xxreg)
>> increases to 8.
>>
>> There's currently not enough space in the NXM_NX class for the new 16
>> registers so we use the NXOXM_ET class instead. According to commit
>> 508a933809f8 ("nx-match: Add support for experimenter OXM.") this is the
>> right class to use for field extensions.
>>
>> NOTE: Commit 85be6684f8af ("meta-flow: Fix the NXM_NX_* names of xxreg2
>> and xxreg3.") had added placeholders for future expansion for four more
>> xxregs (xxreg4-7) in the NXM_NX class. However, since now the
>> new reg16-31 registers are added to the NXOXM_ET class, we also add
>> the corresponding xxreg4-7 to it.
>>
>> [0] https://mail.openvswitch.org/pipermail/ovs-dev/2025-October/426703.html
>> [1] https://mail.openvswitch.org/pipermail/ovs-dev/2025-December/428768.html
>>
>> Suggested-by: Ilya Maximets <[email protected]>
>> Reported-at: https://issues.redhat.com/browse/FDP-2843
>> Signed-off-by: Dumitru Ceara <[email protected]>
>
> Thanks, Dumitru, for working on this change! It looks good to me. There are a
> few small nits, but with those addressed:
>
Hi Eelco,
> Acked-by: Eelco Chaudron [email protected]
>
Thanks for the review!
I have a v3 patch ready where the only changes are the fixes for the two
comments you had below.
But I see now on patchwork that the v2 patch [0] is delegated to Ilya so
I'll wait a bit with posting v3 in case there are more changes required.
Regards,
Dumitru
[0]
https://patchwork.ozlabs.org/project/openvswitch/patch/[email protected]/
>> ---
>> V2:
>> - Addressed Ilya's comments:
>> - retitled commit
>> - updated NEWS item
>> - updated meta-flow comments and documentation
>> - added ovs-ofctl.at and test_ofp.py tests
>> ---
>> NEWS | 1 +
>> include/openflow/nicira-ext.h | 2 +-
>> include/openvswitch/flow.h | 8 +-
>> include/openvswitch/meta-flow.h | 142 +++++++--
>> lib/dpif-netdev-extract-avx512.c | 2 +-
>> lib/flow.c | 20 +-
>> lib/flow.h | 2 +-
>> lib/match.c | 2 +-
>> lib/meta-flow.xml | 66 +++-
>> lib/nx-match.c | 2 +-
>> lib/odp-util.c | 6 +-
>> lib/odp-util.h | 2 +-
>> lib/ofp-match.c | 2 +-
>> ofproto/ofproto-dpif-rid.h | 2 +-
>> ofproto/ofproto-dpif-xlate.c | 2 +-
>> python/ovs/tests/test_ofp.py | 202 +++++++++++++
>> .../ovs_build_helpers/extract_ofp_fields.py | 2 +-
>> tests/ofproto.at | 4 +-
>> tests/ovs-ofctl.at | 284 +++++++++++++++++-
>> 19 files changed, 683 insertions(+), 70 deletions(-)
>>
>> diff --git a/NEWS b/NEWS
>> index ca7e66ab7b45..6bb45fc094e6 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -30,6 +30,7 @@ Post-v3.6.0
>> * The OOT kernel module: was deprecated in v2.15; was last present in
>> the v2.17 release; and is no longer present in any supported release
>> since v2.17 went EOL when v3.5 was released.
>> + - Increased the number of registers to 32.
>
> Maybe add the word ‘OpenFlow’, so people know what registers we talk about?
>
Yes, definitely better.
>
>> v3.6.0 - 18 Aug 2025
>
> [...]
>
>> diff --git a/lib/meta-flow.xml b/lib/meta-flow.xml
>> index 5c57ab08ff18..1ef77d284b42 100644
>> --- a/lib/meta-flow.xml
>> +++ b/lib/meta-flow.xml
>> @@ -2902,10 +2902,20 @@ actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
>> </field>
>>
>> <field id="MFF_REG0" title="Register 0">
>> - This is the first of several Open vSwitch registers, all of which have
>> - the same properties. Open vSwitch 1.1 introduced registers 0, 1, 2,
>> and
>> - 3, version 1.3 added register 4, version 1.7 added registers 5, 6,
>> and 7,
>> - and version 2.6 added registers 8 through 15.
>> + <p>
>> + This is the first of several Open vSwitch registers, all of which
>> have
>> + the same properties. Open vSwitch 1.1 introduced registers 0, 1, 2,
>> + and 3, version 1.3 added register 4, version 1.7 added registers 5,
>> 6,
>> + and 7, version 2.6 added registers 8 through 15, and version 3.7
>> added
>> + registers 16 through 31.
>> + </p>
>> +
>> + <p>
>> + Code points for registers 0 through 15 are defined within NXM_NX
>> code
>> + point prefix, while registers 16 through 31 are defined within
>> + NXOXM_ET starting with NXOXM_ET_REG16 (17), due to limited space
>> + within the NXM_NX class.
>> + </p>
>> </field>
>> <!-- XXX series -->
>> <field id="MFF_REG1" title="Register 1" hidden="yes"/>
>> @@ -2923,6 +2933,22 @@ actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
>> <field id="MFF_REG13" title="Register 13" hidden="yes"/>
>> <field id="MFF_REG14" title="Register 14" hidden="yes"/>
>> <field id="MFF_REG15" title="Register 15" hidden="yes"/>
>> + <field id="MFF_REG16" title="Register 16" hidden="yes"/>
>> + <field id="MFF_REG17" title="Register 17" hidden="yes"/>
>> + <field id="MFF_REG18" title="Register 18" hidden="yes"/>
>> + <field id="MFF_REG19" title="Register 19" hidden="yes"/>
>> + <field id="MFF_REG20" title="Register 20" hidden="yes"/>
>> + <field id="MFF_REG21" title="Register 21" hidden="yes"/>
>> + <field id="MFF_REG22" title="Register 22" hidden="yes"/>
>> + <field id="MFF_REG23" title="Register 23" hidden="yes"/>
>> + <field id="MFF_REG24" title="Register 24" hidden="yes"/>
>> + <field id="MFF_REG25" title="Register 25" hidden="yes"/>
>> + <field id="MFF_REG26" title="Register 26" hidden="yes"/>
>> + <field id="MFF_REG27" title="Register 27" hidden="yes"/>
>> + <field id="MFF_REG28" title="Register 28" hidden="yes"/>
>> + <field id="MFF_REG29" title="Register 29" hidden="yes"/>
>> + <field id="MFF_REG30" title="Register 30" hidden="yes"/>
>> + <field id="MFF_REG31" title="Register 31" hidden="yes"/>
>>
>> <field id="MFF_XREG0" title="Extended Register 0">
>> <p>
>> @@ -2931,8 +2957,13 @@ actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
>> vSwitch already had 32-bit registers by that name, so Open vSwitch
>> uses
>> the name ``extended registers'' in an attempt to reduce confusion.
>> The
>> standard allows for up to 128 registers, each 64 bits wide, but Open
>> - vSwitch only implements 4 (in versions 2.4 and 2.5) or 8 (in version
>> - 2.6 and later).
>> + vSwitch only implements 4 (in versions 2.4 and 2.5), 8 (in version
>> + 2.6 and later), or 16 (in version 3.7 and later).
>> + </p>
>> +
>> + <p>
>> + Code points for all of the extended registers are defined within
>> + OXM_OF_PKT_REG code point prefix.
>> </p>
>>
>> <p>
>> @@ -2961,6 +2992,14 @@ actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
>> <field id="MFF_XREG5" title="Extended Register 5" hidden="yes"/>
>> <field id="MFF_XREG6" title="Extended Register 6" hidden="yes"/>
>> <field id="MFF_XREG7" title="Extended Register 7" hidden="yes"/>
>> + <field id="MFF_XREG8" title="Extended Register 8" hidden="yes"/>
>> + <field id="MFF_XREG9" title="Extended Register 9" hidden="yes"/>
>> + <field id="MFF_XREG10" title="Extended Register 10" hidden="yes"/>
>> + <field id="MFF_XREG11" title="Extended Register 11" hidden="yes"/>
>> + <field id="MFF_XREG12" title="Extended Register 12" hidden="yes"/>
>> + <field id="MFF_XREG13" title="Extended Register 13" hidden="yes"/>
>> + <field id="MFF_XREG14" title="Extended Register 14" hidden="yes"/>
>> + <field id="MFF_XREG15" title="Extended Register 15" hidden="yes"/>
>>
>> <field id="MFF_XXREG0" title="Double-Extended Register 0">
>> <p>
>> @@ -2970,7 +3009,16 @@ actions=clone(load:0->NXM_OF_IN_PORT[],output:123)
>> through <code>reg3</code>, with <code>reg0</code> supplying the
>> most-significant bits of <code>xxreg0</code> and <code>reg3</code>
>> the
>> least-significant. <code>xxreg1</code> similarly overlays
>> - <code>reg4</code> through <code>reg7</code>, and so on.
>> + <code>reg4</code> through <code>reg7</code>, and so on. Open
>> + vSwitch 4 128-bit registers (in versions 2.6 and later) and 8
>
> Should this be “Open vSwitch ‘only implements’ 4”?
>
Ah, yes, it should probably be like that.
>> + (in version 3.7 and later).
>> + </p>
>> +
>> + <p>
>> + Code points for double-extended registers 0 through 3 are defined
>> + within NXM_NX code point prefix, while registers 4 through 7 are
>> + defined within NXOXM_ET starting with NXOXM_ET_XXREG4(33), due to
>> + limited space within the NXM_NX class.
>> </p>
>> </field>
>
> [...]
>
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